- 2070 Asar · 5 marks
PAM versus PWM
Short answer
PAM varies pulse amplitude proportional to message, width constant; PWM varies pulse width, amplitude constant. PAM is simpler but more noise sensitive; PWM offers better noise immunity and is used in motor control. PAM is a step in PCM, PWM needs synchronisation.
Differentiate between PAM and PWM.
PAM (Pulse Amplitude Modulation): the amplitude of a train of constant-width pulses is varied in proportion to the instantaneous message amplitude. PWM (Pulse Width Modulation), also called pulse duration modulation, varies the width of the pulses, while the amplitude and position stay constant.
| Point | PAM | PWM |
|---|---|---|
| Parameter varied | Pulse amplitude | Pulse width (duration) |
| Pulse width and position | Constant | Width varies; position of one edge fixed |
| Noise immunity | Poor: noise adds directly to amplitude | Better: amplitude can be clipped |
| Bandwidth | Lower | Higher (needs steep edges) |
| Transmitted power | Varies with message | Varies with width (average) |
| Generation / detection | Simple: sample and hold | Needs a ramp/comparator circuit |
| Synchronisation | Not needed | Needed to find the edge |
| Use | First step of PCM, TDM | Motor speed control, DC-DC converters, servo |
✓ Answer checked by Claude Sonnet 5.5
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